1. Technical Field
The present invention relates to an optical position detection device for optically detecting a position of a target object, and a display system with an input function provided with the optical position detection device.
2. Related Art
As the optical position detection device for optically detecting the target object, there is proposed, for example, a device (see, e.g., JP-T-2003-534554 (Patent Document 1) in which detection lights are emitted respectively from a plurality of point light sources toward the target object via a light transmissive member, and then the detection lights reflected by the target object are transmitted through the light transmissive member, and then detected by a light receiving element. Further, there are also proposed optical position detection devices using a method of emitting the detection lights, which are emitted respectively from the plurality of point light sources, via a light guide plate, and then detecting the detection lights reflected by the target object with the light receiving element (see JP-A-2010-127671 (Patent Document 2) and JP-A-2009-295318 (Patent Document 3)).
In such optical position detection devices, the position of the target object is detected based on a result of comparison between a light reception intensity in the light receiving element when lighting some of the plurality of point light sources and alight reception intensity in the light receiving element when lighting some other of the plurality of point light sources.
However, in the optical position detection devices described in Patent Documents 1 through 3, there is a problem that a range in which the position of the target object can be detected is narrow. Specifically, in the optical position detection device described in Patent Document 1, the detection light emitted from the point light source is used. Therefore, since an emission angular range itself of the detection light is narrow, the range in which the position of the target object can be detected is narrow. Further, in the optical position detection devices described in Patent Documents 2 and 3, although the detection light emitted from the point light source is emitted via the light guide plate, and therefore the detection light can be emitted throughout a relatively wide range, attenuation of the detection light while propagating inside the light guide plate is inevitable. Therefore, since it is difficult to form a predetermined light intensity distribution with a sufficient intensity level throughout a wide range, the range in which the position of the target object can be detected is narrow.